Metal structures which are self-destructible by chemical corrosion

ABSTRACT

A metal laminate is provided which will deteriorate, at least in part, after the interior of the laminate is contacted by moisture. Self-destructible containers are fabricated of this structural laminate. The laminate includes at least two metal layers. Preferably, both layers are comprised of the same metal. Positioned between the metal layers is at least one layer of a composition capable of chemically corroding the metal layers when the composition is contacted with moisture. A preferred metalcorroding composition is an inorganic salt, such an ammonium chloride.

United States Patent 7 1 1 George 1451. July ,10, 1973 [54] METAL STRUCTURES WHICH ARE lSquletsi :36 ru en 7 SELF DESTRUCTIBLE BY CHEMICAL 3,388,824 6/1968 Hazard... 161/213 CORROSION 3,415,402 12/1968 Webber 220/64 [7.51 ff PeFcy 9 18? fl ff M FOREIGN PATENTS OR APPLICATIONS 1 1 Assigneei e DvwChpmical p y, 368,816 3/1932 Great Britain 204/197 M1dland, M1611. 853,946 1 1/ 1960 Great Britain 204/ 197 t Notice: The portion of the term of this patent subsequent to Dec. 21, 1988 OTHER PQBUCATPNS s 666 e Perry, John 11., Chemical Engmeers Handbook, [22] .Filed: M". 5, 9 xlcGraw-Hfll, New York (1963), p. 23-29,20 relied [21 Appl. No; 16,725

7 Primary Examiner--George F. Lesmes 52 us. (:1 220/10 161/216, 161/225, m 'T B' 220,9 M, 220/9 R 250/83 ZZOIDIG 30, Attorney-Gnswold and Burdlck, V. Dean Clausen and 229 35 MF, 161/213, 161/220 [51] Int. C1..... B321) 15/04, B321) 15/12, 865d 7/22 [58] Field 61 Search 161/216, 225, 22s, ABSTRACT 2 a A metal laminate is provided which will deteriorate, at

0, 9 9 R least in part, after the interior of the laminate is contacted by moisture. Self-destructible containers are fabricated of this structural laminate. The laminate in- References C'ted eludes at least two metal layers. Preferably, both layers UNITED STATES PATENTS v are comprised of the same metal. Positioned between 1,811,160 6/1931 Stevenson 204/197 the metal layers is at least one layer of a cvmpvsition 1,837,051 12/1931 Kohman..... 204/197 capable of chemically corroding the metal layers when 2,490,973 1949 OSleIheld 204/197 the composition is contacted with moisture. A pre- 2,722,3l1 11/1955 Mormon 206/46 M ferred metal-corroding composition is an inorganic 3,152,717 10/ 1964 Schwaiger 220/64 salt, such an ammonium chloride 3,210,840 10/1965 Ulam 29/1962 3,265,598 8/1966 Rohrman 204/141 8 Claims, 2 Drawing Figures PATENTEU JUL 1 01m METAL STRUCTURES WHICH ARE SELF-DESTRUCTIBLE BY CHEMICAL CORROSION BACKGROUND OF THE INVENTION The invention relates broadly to self-destructible metal structures comprising two or more metal layers and one or more layers of a metal-corroding composition positioned between each pair of metal layers. A specific embodiment of the invention concerns a metal container fabricated of such a structural laminate.

Most non-returnable metal containers in use today require a relatively long period of time to deteriorate when the container is discarded. With millions of such containers being discarded each day, the problem of sufficient space to dispose of the refuse is one of growing concern. It would be desirable, therefore, to pro vide a metal container which after being opened would deteriorate within a few months in an outdoor environment.

OBJECTS Accordingly, a principal object of the invention is a self-destructible metal laminate suitable for the fabrication of containers, particularly containers which after being opened will deteriorate substantially more rapidly than the prior metal containers.

A more specific object is a metal container fabricated from a laminate comprising metal layers and a metalcorroding composition, particularly a container which will undergo deterioration, aided by chemical corrosion, upon contacting the metal-corroding composition with moisture.

SUMMARY OF THE INVENTION Broadly, the invention provides a structural metal laminate useful for the fabrication of metal containers, which laminate undergoes corrosive deterioration upon contacting the interior of thelaminate with moisture. A specific embodiment of the invention contemplates a container in which at least one wall member of the container comprises the structural laminate described herein. The preferred laminate includes at least two metal layers and at least one layer of a metal-corroding composition which is positioned between the metal laysition which, when contacted with moisture, will chem ically corrode each of the metal layers.

FIG. 1 is a front elevation view, partly in section, of a container fabricated from the structural laminate described herein.

FIG. 2 is an enlarged section view of the chime portion of the container, as illustrated in FIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT In the drawing numeral indicates generally a cylindrical metal container. Basically, container 10 comprisesa side wall 11, a top wall 12 and a bottomwall 13. In the embodiment of the invention, as illustrated herein, the container walls comprise a three-layer structural laminate. The laminate is fabricated of at least two metal layers 14, 15, and at least one layer 16 of a metal-corroding composition, which is positioned between the metal layers. In fabricatingthe container 10, the joining of side wall 11 with top wall 12 forms a chime portion, indicated generally by numeral 17.

ers of the laminate. The corroding medium is a compo- The metal layers of the laminate structure may be single metals, metal alloys, clad metals or the like. Preferably, each layer will be the same kind of metal, but the invention also contemplates a laminate structure utilizing layers of different metals, or individual layers of more than one metal, such as clad and galvanized metals. The choice of metals to be used will depend on such factors as the suitability of the metal for container fabrication, cost of the metal, strength requirements of the laminate structure, type of material to be packaged in the container, and the like. Alloys of iron, such as steel, and alloys of magnesium or aluminum are pre ferred in fabricating a laminate structure in which the same metal is used for each layer. For a laminate structure using layers of different metals, a typical example would be a layer of steel and a layer of an aluminum alloy.

With regard to the metal layers, it is preferred to use, in the case of aluminum, alloys containing at least 50 percent aluminum, and more preferably about 85 percent aluminum. Typical of the aluminum alloys which may be used are those compositions listed in the Regis tration Record of Aluminum Assoc. Alloy Designations and Chemical Composition Limits: for Wrought Aluminum Alloys. Particularly suitable compositions are those designated by the following Aluminum Assoc. numbers: 1100, 2017, 3002, 4045, 5052, 5056, 6061,, 7075 and 8001. Preferred magnesium alloy compositions for use in the laminate structure are those which contain at least 50 percent magnesium and preferably about 85 percent magnesium. Especially suitable magnesium alloys are those listed by the American Society for Testing Materials under the following designations:

MIA, AZ31B, A3A, AZ61B, AZSOA, ZKA and ZElOA (see Metals Hankdbook, Amer. Soc. for Metals). Although thickness of the individual metal layers is not critical, the usual materials are metal foils less than one-eighth inch inthickness. Preferably, the'container laminate, which includes the metal layers 14, 1.5, and the corroding composition 16, is a generally flexible structure having an over-all or total thickness of not more than about one-fourth inch.

In fabricating a container in which the same metal is used for each layer of the laminate structure, the inner layer 14 of top wall 12 and the outer layer 15 of side wall 11 are normally joined in face-to-face contact at a joint J within the chime portion (note FIG. 2). In fabricating a container in which different metals are employed for each layer in the laminate structure, such as steel and aluminum, for example, the layers are separated at joint J with a non-conductor material 18. The non-conductor material 18 prevents electron :flow between the unlike metal layers and thereby precludes the possibility of galvanic corrosion of the container laminate. In general, any material capable of providing electrical insulation between the metal layers at joint J may be used. Conventional rubber-based adhesives are preferred.

chloride and magnesium chloride. Suitable acid compositions which may be used are organic acids, such as tartaric acid and citric acid. Representative of bases which may be used for the corroding composition are the soluble metal hydroxides, the preferred compounds being sodium hydroxide, potassium hydroxide, lithium hydroxide and barium hydroxide.

Positioning or layering of the metal corroding com position between the metal layers of the laminate structure may take several forms. For example, the corroding composition, in the form of discrete particles, may be adhered to the inner surfaces of the metal layers. In another form the discrete particles may be placed loosely between the metal layers. In still another form the composition may be impregnated onto a bibulous carrier material and the carrier strip sandwiched between the metal layers of the laminate. Use of a carrier strip impregnated with the corroding composition is preferred, since the bibulous carrier material can act as a wick to help carry moisture between the metal layers of the laminate after the container is opened.

Suitable carrier materials for the corroding composition include absorbent papers, such as paper toweling; water permeable hydrophilic adhesives, porous polymeric films, such as open-cell plastic films; and soluble polymeric films of water-soluble film formers, such as methylcellulose, hydroxyethyl cellulose, polyvinyl alcohol, polyvinylpyrolidone and polyvinyloxazolidone. It will be readily appreciated that the corroding composition must be sealed between the metal layers of the laminate to prevent the composition from coming into premature contact with moisture.

To initiate deterioration of the laminate, as in the walls of a discarded container, a preferred means of severing the laminate structure is a tear strip (not shown), which is integrally formed in top wall 12 of the container. Although a tear strip is preferred, any device which will effectively sever or puncture the container laminate, such as a can opener, may be used to achieve communication between the corroding composition and environmental moisture.

When the container laminate is severed and the composition is wetted with moisture, which may be provided as rain, snow, dew, condensate, atmospheric moisture, liquid from the contents of the container, or

the like, a solution corrosive to the metal layers is formed. The resulting chemical corrosion usually initiates a simultaneous deterioration of each metal layer. However, with some combinations of metals and corroding media, particularly where different metals are employed, each metal layer may deteriorate at a different rate.

According to one embodiment of the invention, the carrier strip is held in place between the metal layers during fabrication of the laminate structure by an adhesive applied in spots to opposite sides of the strip. In general, any adhesive which will secure the carrier strip to the metal layer long enough to form the laminate structure is suitable. Typical adhesives which may be used are the solvent cements, such as Duco (brand) cement.

In the container embodiment illustrated herein, referring particularly to FIG. 2, it will be noted that perforations 19 extend completely through the innermost double metal layer joint formed in chime portion 17. Perforations 19 provide communication between top wall 12 and side wall 11 of the container, which enhances migration of moisture from the top wall to the side wall once the container laminate is severed. With regard to positioning of perforations 19, it will be appreciated that these openings must be placed at a point in the chime portion 17 which is sealed off from the contents of the container. Positioning of the perforations in the manner indicated in FIG. 2 will prevent any moisture in the container contents from contacting the corroding composition 16 before the container is opened, thus avoiding premature initiation of the corrosive reaction.

Additional embodiments of the invention include laminates and containers fabricated therefrom in which the laminate is a multi-layer structure comprising more than two metal layers and one or more metal-corroding compositions positioned between each pair of metal layers.

The following examples are given to illustrate the invention, but arenot to be construed as limiting the invention to the embodiments described herein.

EXAMPLE I The laminate structure was cut into two separate sections, each section measuring about 1 k in. wide and 3 in. long. One section was stood upright in a shallow pool of water to wet the paper layer exposed along the bottom edge of the section and the section was allowed to stand in the water for about three months. After two weeks the laminate section standing in water was observed to be severely corroded. At the end of three months the metal layers had completely converted to a corrosive residue. The other laminate section was allowed to lay on a bench at room temperature for the same three-month period. At the end of the period no visible evidence of corrosion could be detected on the section which had lain on the bench.

EXAMPLE II A sheet of paper towel about 2 in. wide and 3 in. long was soaked in a saturated aqueous solution of tartaric acid and dried at room temperature. To one side of the paper sheet was cemented a sheet of magnesium alloy (AZ61) about 2 in. wide, 3 in. long and 0.003 in. thick. An identical sheet of magnesium alloy was adhered to the opposite side of the paper sheet, to complete the three layer laminate.

The laminate structure was cut into two separate sections, each section measuring about I in. wide and 3 in. long. Following the procedure of Example I, one section was placed on edge in water and held in this position for about 2 days. For the same 2-day period the other section was allowed to lay on a bench at room temperature. At the end of two days each section was checked for corrosion. Both metal layers of the laminate section which had stood in water were badly corroded. No corrosion was visible on the section which had lain on the bench.

EXAMPLE III A sheet of paper towel about 2 in. wide and 3 in. long was soaked in a saturated aqueous solution of ammo nium chloride and dried at room temperatpre. A sheet of magnesium alloy (A261) about 2 in. wide, 3 in. long and 0.003 in. thick was cemented to one side of the paper sheet. An identical sheet of magnesium alloy was adhered to the opposite side of the paper sheet to complete the three layer laminate.

The laminate structure was cut into two separate sections, each section measuring about I in. wide and 3 in. long. In the manner described in Example I, one section was stood on edge in water and held in this position for about 24 hours. The other section was allowed to lay on a bench at room temperature for the same 24-hour period. At the end of 24 hours the metal layers of the section standing in water had been almost completely consumed by corrosion. The section which had lain on the bench was examined and no corrosion could be detected.

What is claimed is:

1. A metal container having at least one wall member fabricated of a structural laminate consisting essentially of:

two metal layers; and

one layer of a metal-corroding composition which is positioned between the metal layers, which is noncorrosive to metals in a dry condition, and which is capable of chemically corroding each of the metal layers when contacted with moisture.

2. The container of claim 1 which includes means integral with the laminate structure for severing a portion of the laminate.

3. The container of claim 1 'in which the over-all thickness of the laminate is not more than about 1/4 inch.

4. The container of claim 1 in which the metalcorroding composition is sealed from the atmosphere.

5. The container of claim 1 in which the metalcorroding composition is impregnated onto a strip of bibulous material.

6. The container of claim 1 in which the metal layers are ferrous alloy metals and the corroding composition is ammonium chloride.

7. A metal container having at least one side wall member, a top wall member and a bottom wall member, the said wall members fabricated of a structural laminate consisting essentially of:

two metal layers; and

one layer of a metal-corroding composition which is positioned between the metal layers, which is noncorrosive to metalsin a dry condition, and which is capable of chemically corroding each of the metal layers when contacted with moisture.

8. The container of claim 7 which includes a chime portion formed by the juncture of' the top wall member with the side wall member, wherein adjacent metal layers in the chime portion have at least one perforation therethrough to enhance moisture communication between the said top wall member and side wall member. 

2. The container of claim 1 which includes means integral with the laminate structure for severing a portion of the laminate.
 3. The container of claim 1 in which the over-all thickness of the laminate is not more than about 1/4 inch.
 4. The container of claim 1 in which the metal-corroding composition is sealed from the atmosphere.
 5. The container of claim 1 in which the metal-corroding composition is impregnated onto a strip of bibulous material.
 6. The container of claim 1 in which the metal layers are ferrous alloy metals and the corroding composition is ammonium chloride.
 7. A metal container having at least one side wall member, a top wall member and a bottom wall member, the said wall members fabricated of a structural laminate consisting essentially of: two metal layers; and one layer of a metal-corroding composition which is positioned between the metal layers, which is non-corrosive to metals in a dry condition, and which is capable of chemically corroding each of the metal layers when contacted with moisture.
 8. The container of claim 7 which includes a chime portion formed by the juncture of the top wall member with the side wall member, wherein adjacent metal layers in the chime portion have at least one perforation therethrough to enhance moisture communication between the said top wall member and side wall member. 